J. Wilson Quail

Cytotoxic 2,6-bis(arylidene)cyclohexanones and related compounds

A number of 2-arylidenecyclohexanones 1, 2, 6-bis(arylidene)cyclohexanones 2 and related Mannich bases 3-5 were prepared. Various torsion angles as well as atomic charges on olefinic carbon atoms were determined by molecular modelling on all compounds. These molecules showed cytotoxicity towards murine P388 and L1210 cells as well as to human Molt 4/C8 and CEM T-lymphocytes. The average cytotoxicity of the dienones 2 was more than three times greater than was found with the monoarylidene analogues 1, and, in general, were slightly more cytotoxic than the Mannich bases 3-5. A number of the compounds displayed potency towards a panel of human tumour cell lines and most of the representative compounds in series 2-5 were selectively toxic to colon cancers and leukaemic cells.

Structure, chemistry, and biological activity of pseudophomins A and B, new cyclic lipodepsipeptides isolated from the biocontrol bacterium Pseudomonas fluorescens

Pseudophomins A and B are cyclic lipodepsipeptides isolated from Pseudomonas fluorescens strain BRG100, a bacterium with potential application for biocontrol of plant pathogens and weeds. Their chemical structures were established by a combination of spectroscopic data, X-ray crystallography, and selective chemical degradation. This unique chemical degradation allowed the unambiguous determination of the absolute configuration of the amino acid residue Leu-1, due to gamma-lactam formation followed by selective cleavage of the adjacent N(8)-C(7) bond. To the best of our knowledge this is the first application of gamma-lactam formation to the determination of absolute configuration of an adjacent amino acid. Pseudophomin B showed higher antifungal activity against the phytopathogens Phoma lingam/Leptosphaeria maculans and Sclerotinia sclerotiorum than pseudophomin A, and is likely to be the main component responsible for the antifungal activity of EtOAc extracts of strain BRG100. By contrast, pseudophomin A showed stronger inhibition of green foxtail (Setaria viridis) root germination than pseudophomin B.

The cytotoxic properties and preferential toxicity to tumour cells displayed by some 2,4-bis(benzylidene)-8-methyl-8-azabicyclo[3.2.1] octan-3-ones and 3,5-bis(benzylidene)-1-methyl-4-piperidones

This study demonstrated that replacement of the axial protons on the C2 and C6 atoms of various 1-methyl-3,5-bis(benzylidene)-4-piperidones 3 by a dimethylene bridge leading to series 2 lowered cytotoxic potencies. Four compounds 2a and 3a-c emerged as lead molecules based on their toxicity towards different neoplasms and their selective toxicity for malignant rather than normal cells. Some possible reasons for the disparity between the IC(50) values in the two series of compounds are presented based on molecular modeling, logP values and respiration in rat liver mitochondria.

The 1·6 Å structure of histidine-containing phosphotransfer protein HPr from Streptococcus faecalis

The histidine-containing phosphocarrier protein (HPr) is a central component of the phosphoenolpyruvate: sugar phosphotransferase system (PTS) that transports carbohydrates across the cell membrane of bacteria. The three-dimensional structure of Gram-positive Streptococcus faecalis HPr has been determined using the method of multiple isomorphous replacement. The R factor for all data is 0.156 for S. faecalis HPr at 1.6 A resolution with very good geometry. The overall folding topology of HPr is a classical open-faced beta-sandwich, consisting of four antiparallel beta-strands and three alpha-helices. Remarkable disallowed Ramachandran torsion angles of Ala16 at the active center, revealed by the X-ray structure of S. faecalis HPr, demonstrate a unique example of torsion-angle strain that is likely involved directly in protein function. A brief report concerning the torsion-angle strain has been presented recently. A newly-determined pH 7.0 structure is shown to have the same open conformation of the active center and the same torsion-angle strain at Ala16, suggesting that pH is not responsible for the structural observations. The current structure suggests a role for residues 12 and 51 in HPrs function, since they are involved in the active center through direct and indirect hydrogen-bonding interactions with the imidazole ring of His15. It is found that Ser46, the regulatory site in HPr from Gram-positive bacteria, N-caps the minor alpha-B helix and is also involved in the Asn43-Ser46 beta-turn. This finding, in conjunction with the proposed routes of communication between the regulatory site Ser46 and the active center in S. faecalis HPr, provides new insight into the understanding of how Ser46 might function. The putative involvement of the C-terminal alpha-carboxyl group and the related Gly67-Glu70 reverse beta-turn with respect to the function of HPr are described.

Cytotoxic N-[4-(3-aryl-3-oxo-1-propenyl)phenylcarbonyl]-3,5-bis(phenylmethylene)-4-piperidones and related compounds

A series of 4-carboxychalcones 1 were prepared and coupled to 3,5-bis(phenylmethylene)-4-piperidone (2) giving rise to a novel series of N-[4-(3-aryl-3-oxo-1-propenyl)phenylcarbonyl]-3,5-bis(phenylmethylene)-4-piperidones (3). Molecular simplification of the amides 3 led to the formation of the corresponding N-(3-aryl-1-oxo-2-propenyl)-3,5-bis(phenylmethylene)-4-piperidones (4). A cytotoxic evaluation of the compounds in series 1-4 utilized murine P388 and L1210 cells as well as human Molt 4/C8 and CEM T-lymphocytes. In general, the compounds displayed significant toxicity; the IC(50) values of 54% of the enones were less than 10 microM when all four screens were considered and less than 1 microM for all members of series 3 in the P388 assay. Various correlations were established between the potencies of the compounds in series 1, 3 and 4 and the Hammett sigma, Hansch pi and molecular refractivity constants of the aryl substituents. Several torsion angles and interatomic distances of five representative compounds in series 3 and 4 were determined by X-ray crystallography, some of which contributed to the observed bioactivity. The marked cytotoxicity and lack of murine toxicity of most of the compounds described in this study, as well as their selective toxicity towards different tumour cell lines, revealed that development of the enones 2-4 as novel candidate antineoplastic agents should be pursued.

Cytotoxic 1,3-diarylidene-2-tetralones and related compounds

A number of 1,3-arylidene-2-tetralones 1, 2 and 4 were synthesised and demonstrated cytotoxic activity towards murine P388 and L1210 cells as well as human Molt 4/C8 and CEM T-lymphocytes. In general, the related 1-arylidene-2-tetralones 3 possessed lower potencies in these screens than the compounds in series 1 and 4. Approximately, half of the compounds were evaluated against a panel of human tumour cell lines. In this screen, most of the enones were more cytotoxic than the established anticancer agent melphalan and some demonstrated selective toxicity towards leukemic and colon cancer cells. The modes of action of representative compounds include interfering with the biosyntheses of nucleic acids and proteins as well as altering redox potentials. The compounds were well tolerated when administered intraperiteonally to mice. Thus these novel enones are promising prototypic molecules due to their potent cytotoxic properties and lack of significant murine toxicity.

Anticonvulsant activity of various aryl, arylidene and aryloxyaryl semicarbazones

Abstract A number of aryl, arylidene and aryloxyaryl semicarbazones were evaluated as candidate anticonvulsants. In particular, insertion of an olefinic group between the carbimino carbon atom and an aryl ring (referred to as the proximal ring) led to series 6 in which there was retention in activity and 6b,c were shown to be useful lead molecules. At the doses utilized, neurotoxicity was absent in these compounds when given orally to rats. Attachment of a 2-naphthyloxy group at the 4 position of the proximal ring gave 7 whose high activity in the rat oral maximal electroshock (MES) screen suggested that the binding site of the second aryl ring was capable of accommodating groups with molecular refractivity values of over 40. The greatest activity was displayed by a series of aryloxyaryl semicarbazones 8 which had oral activity in the MES screen substantially greater than phenytoin and with protection indices of over 100. A binding site hypothesis formulated as a result of the biodata generated was in accord with the information obtained by X-ray crystallography.

Phomalairdenone: a new host-selective phytotoxin from a virulent type of the blackleg fungus Phoma lingam.

The chemical structure and bioactivity of phomalairdenone (7), a new sesquiterpenic host-selective phytotoxin produced by an unusual virulent type isolate of the blackleg fungus [Phoma lingam, perfect stage Leptosphaeria maculans (Desm.) Ces. et de Not.] are reported.

Synthesis and biological activity of tetralone abscisic acid analogues

Bicyclic analogues of the plant hormone abscisic acid (ABA) were designed to incorporate the structural elements and functional groups of the parent molecule that are required for biological activity. The resulting tetralone analogues were predicted to have enhanced biological activity in plants, in part because oxidized products would not cyclize to forms corresponding to the inactive catabolite phaseic acid. The tetralone analogues were synthesized in seven steps from 1-tetralone and a range of analogues were accessible through a second route starting with 2-methyl-1-naphthol. Tetralone ABA 8 was found to have greater activity than ABA in two bioassays. The absolute configuration of (+)-8 was established by X-ray crystallography of a RAMP hydrazone derivative. The hydroxymethyl compounds 10 and 11, analogues for studying the roles of 8- and 9-hydroxy ABA 3 and 6, were also synthesized and found to be active.

Solvent effects on the redox properties of ferrocenoyl-dipeptides

The preparation and characterization of the novel ferrocenoyl-dipeptides, Fc-Asp(OBzl)-Asp(OBzl)-OBzl (5), Fc-Asp(OBzl)-Glu(OEt)-OEt (6) and Fc-Asp(OBzl)-Cys(Bzl)-OMe (7) are reported. In addition, Fc-Asp(OBzl)-OBzl (4) and its free acid, Fc-Asp(OH)-OH (8), were prepared. A crystal structure determination of 8 revealed an extensive H-bonding network involving a solvent molecule and adjacent molecules of 8 and suggests that these complexes are able to form strong hydrogen bonds with solvent molecules. All compounds show reversible one-electron oxidations in solution. The half-wave potential is strongly influenced by the nature of the solvent and correlates with the hydrogen donor ability α of the Kamlet–Taft formalism.